Originally Posted by Hugh Jarse
The thing that gets me is that the determination of "severe icing" seems to be subjective, and up to the crew to decide.
Therefore, one crew's assessment of conditions described as "severe" might be interpreted by another as "moderate" when flying through the same airspace, and vice versa.
I would think that the Q400 flight manual gives guidance as to what constitutes severe icing. In the little Dashes severe icing is considered to be when ice starts forming on the pilot's side window aft of the leading edge and when significant ice forms on the prop spinner aft of the nose toward the blades. It's still subjective in that crews of different aircraft types might have different ideas as to the severity of the ice, but two crews flying the same type through the same conditions should come to a common answer.